Am I supposed to be showing a baby bump yet? ?

Everyone is different. With both of mine I bloated up right away just from water retention and had to buy new jeans, and with my 2nd I definitely had a bump by 13 years (with my first I was just in that awkward "pregnant or just chubby?" stage). Other women can be halfway through their pregnancies and still wearing most of their normal clothes. How baby fits in your body has to do with your skeletal and muscular structure more than anything else, and even women who are the same height and same weight can have drastically different-looking pregnancies. As long as your OB is certain that baby is growing normally, there's no need to worry if you're on the smaller side. 

you'll start showing sooner or later

Most women will notice the first signs of a bump early in the second trimester, between weeks 12 and 16.